The present invention relates to a new process for dyeing polyamide fibers with acid dyestuffs, which gives dyeings having improved light-fastness.
For most intended uses as textiles, polyamide fibers have to be delustred, which is achieved industrially by the addition of titanium dioxide pigments.
However, it is generally known that the presence of titanium dioxide in polyamide fiber has an adverse effect on its photostability. The more pigmented a fiber is, the less light-fast it is. Efforts are known from the literature to improve the light-fastness of non-dyed polyamide fibers either by addition of metal ions, such as, for example, Mn.sup.2+, Cu.sup.+, Cu.sup.2+ or Co.sup.2+, to the spinning melt or by surface treatment of the polyamide fiber (Textilveredelung 20, No. 11 (1985), 346 and JP 57 089 654).
Attempts have furthermore been made to improve the light-fastness of dyeings on polyamide by adding copper(II) salts to the dyebath (Textitveredelung 20, loc. cit.). A large excess of copper(II) salt is required here, because of a lack of affinity of the copper ions for the fiber. Organic copper complex compounds have a better fiber affinity. It is known to add such copper complex compounds, in particular those of diazomethine derivatives, to the dyebath to improve the light-fastness of the dyeing (Textilveredelung 24, No. 5 (1989), 182). However, the processes known from the prior art do not satisfy all the requirements. In particular, when dyeing polyamide microfibers which have a high degree of delustring, only dyeings of inadequate light-fastness have been obtainable to date with acid dyestuffs at the acid pH values necessary for these dyestuffs.
The organic copper complexes known from the prior art exhibit little improvement or no-improvement at all in the light-fastness of the resulting dyeing when used for dyeing with acid dyestuffs.
Since particularly deep color shades can be achieved with acid dyestuffs on polyamide, there was thus the need for a dyeing process for acid dyestuffs which gives dyeings of improved light-fastness.